In high voltage/high power electronic devices, a performance characteristic of importance may be the breakdown characteristics of the device. For example, the maximum reverse bias blocking voltage sustainable by the device may limit the potential applications for the device. In conventional transistors, the structure of the device may result in a breakdown voltage that is less than the breakdown voltage of the device. For example, in a conventional U-metal oxide semiconductor field effect transistor (UMOSFET), field crowding may result at a corner of the gate trench such that breakdown occurs in the region of the field crowding rather than in the bulk material. Various structures have been proposed in different types of transistors to provide breakdown voltages of the transistors that approach the bulk breakdown voltage of the materials used in the transistors.
Current aperture transistors have been proposed as a potential approach to achieve near bulk breakdown limits in nitride-based devices. FIG. 1 illustrates a conventional current aperture transistor 10. As seen in FIG. 1, the current aperture transistor 10 includes a silicon doped GaN drain layer 12 with spaced apart regions of insulating GaN 14 that form the current aperture region 30. The current aperture region 30 is part of a regrown unintentionally doped GaN layer 16 that has an AlGaN layer 18 formed thereon so that a two-dimensional electron gas (2DEG) forms at the interface between the unintentionally doped GaN layer 16 and the AlGaN layer 18. A gate contact 24 and a source contact 22 are provided on the AlGaN layer 18 and a drain contact 26 is provided on the silicon doped GaN layer 12.
In operation, electrons from the source contact 22 flow along the 2DEG and through the current aperture 30 to the drain contact 26. The Schottky gate contact 24 modulates the charge in the 2DEG to control the flow of current through the aperture. Because the pinched off region is located beneath the gate, substantial charge does not accumulate at the gate edge. Thus, the high field region may be buried in the bulk material. Further details on current aperture transistors may be found in Ben-Yaacov et al., “AlGaN/GaN current aperture vertical electron transistors with regrown channels”, Journal of Applied Physics, Vol. 95, No. 4, 15 Feb. 2004, pp. 2073-78.